1. Field of the Invention
This invention relates to a rotating head apparatus used for, in for instance, a magnetic recording apparatus.
2. Description of the Prior Art
The conventional rotating head apparatus hitherto used has a structure as shown in FIG. 23 and FIG. 24. That is, a rotary cylinder 2 which rotates at 1,000 rpm -2,000 rpm relative to a magnetic tape 1 and a stationary cylinder 3, which does not rotate, guide the magnetic tape 1. On the stationary cylinder 3, a lead 4 is provided for regulating the position of the magnetic tape 1 at the time of running. A rotating head 5 mounted on the rotary cylinder 2 is projected by several 10 microns outward from the periphery of the rotary cylinder 2. The number 6 represents a recess in which the magnetic head is disposed.
The rotary cylinder 2 rotates at 1,000-2,000 rpm and at the same time the magnetic tape 1 runs while being wound slantwise (helical) with a specified angle around the rotary cylinder 2 and the stationary cylinder 3 with a specified tape tension. The rotating head 5, which is mounted on the rotary cylinder 2 by projecting itself by several 10 microns outward from the periphery of the rotary cylinder, rotates by making contact with the tape 1.
With the conventional structure, an air film 7 is formed on the periphery of the cylinder as shown in FIG. 24. So, the contact state of the rotating head 5 with the magnetic tape 1 changes at different positions in the helical path, for example at a tape contact inlet (A), a tape contact middle position (B) and a tape contact outlet (C). Thus, as shown in FIGS. 25(A)-25(C), assuming that an angle .alpha. is be an angle formed in the tape width direction, perpendicular to the tape running direction, by the center line n of the magnetic gap of the rotating head and a normal line m to a tape-contacting surface of the rotating head contacting the magnetic tape, the angle .alpha. changes depending on the scanning position of the rotating head.
Furthermore, because the state of air film 7 varies as the cylinder rotating speed varies, there is such a problem that the angle o formed between the lines m and n varies in accordance with the variations in the cylinder rotating speed.
Experimental data is shown in FIGS. 28A to FIG. 31C on the contact state made between rotary head 5 and tape 1. The data in FIGS. 28A to FIG. 31C represent measurements of a distance between micrometer 9 and the tape 1 at the respective points of the tape contact inlet (A), middle position (B) and tape contact outlet (C), by scanning with the micrometer in a cross direction of the tape and also by changing the rigidity of the tape and the cylinder rotating speed in an experimental installation shown in FIG. 27. Experimental conditions are shown respectively as follows: in FIG. 28 cylinder rotating speed 1,800 rpm, high tape rigidity; in FIGS. 29A-29C, cylinder rotating speed is 1,800 rpm, at a low tape rigidity; in FIGS. 30A-30C, cylinder rotating speed 5,400 rpm, low tape rigidity; and in FIGS. 31A-31C, the cylinder rotating speed is 5,400 rpm, at a high speed rigidity. FIGS. 32A and 32C show experimental data, obtained through the use of an interference fringe, of the contact state between the head and the tape at the position of the tape contact inlet (A) and the tape contact outlet (C), and from these figures it becomes clear that the center of contact between the head and the tape at the tape contact inlet (A) locates higher than the head end, while at the tape contact outlet (C) the center of contact between the head and the tape locates lower than the head end. From this experimental data, it is understood that the contact state between the tape and the head varies with the variation of the cylinder rotating speed, tape rigidity, and the scanning position of the rotating head.
FIGS. 25(A)-25(C) and FIGS. 26A-25(C) show examples of contact states between the rotating head 5 and tape 1 of the conventional rotating head apparatus, in which the tape rigidity of FIGS. 26(A)-26(C) is higher than that of FIG. 25, where .alpha. is the angle formed between the lines m and n. As the space to the tape 1 near the magnetic gap becomes larger in accordance with the angle .alpha. which becomes larger, signal recording and reproducing performances reduce with larger space loss. With the conventional rotating head apparatus, the existence of larger value .alpha. (for example, at the tape inlet (A) and the tape outlet (C) in FIG. 24) often causes the problem of lowering the signal recording and reproducing performances. The variations in tape rigidity and thickness following the variation in the kind of the tape also cause a problem of changing the value .alpha. as shown in FIGS. 25(A)-25(C) and FIGS. 26(A)-26(C).
Assuming that an angle .beta. is an angle formed in the tape longitudinal direction, parallel to the tape running direction, by the center line n of the magnetic gap of the rotating head 5 and the normal line m to the contact surface between the tape 1 and the rotating head 5, the space to the tape 1 near the magnetic gap becomes larger as the value of .beta. becomes larger, so that space loss becomes larger, thereby lowering the performances of signal recording and reproducing. Such a case occur frequently such that the value of .beta. does not become 0 as shown in FIGS. 33A-33C and FIGS. 34A-34C. FIG. 35 shows measurements of the value .beta. made in accordance with the cylinder rotating speed and scanning position of the head. The value of .beta., like that of .alpha., changes in accordance with the variations of the cylinder rotating speed, tape rigidity, and scanning position of the rotating head.
To prevent the change of the angle .alpha. or the angle 8 dependent on the scanning position of the rotating head, such a method is known that moves the rotating head in the tape width direction or in the tape longitudinal direction according to the scanning position of the rotating head as shown in Japanese Patent Publication No. 61-144721 published on Jul. 2, 1986 and Japanese Patent Publication No. 63-4249 published on Jan. 28, 1988.
Japanese Patent Publication No. 61-144721 discloses a rotating head apparatus which has a means for detecting a rotational position of the rotating head relative to the stationary cylinder, and a means for moving the rotating head in a direction parallel to the tape running direction according to the detected rotational position of the rotating head so as to keep an optimum contact (.beta.=0) between the rotating head and the magnetic tape at any scanning position. Japanese Patent Publication No. 63-4249 discloses a rotating head apparatus which has a means for detecting a rotational position of the rotating head relative to the stationary cylinder, and a means for moving the rotating head in a direction parallel to the tape width direction according to the detected rotational position of the rotating head so as to keep an optimum contact (.alpha.=0) between the rotating head and the magnetic tape at any scanning position.
To move the rotating head as above, the apparatus has a circuit for generating from an output signal of the rotational position detecting means a drive voltage signal which is a cyclic saw-tooth waveform signal synchronized with the rotation of the rotating head. The rotating head is driven by the drive voltage signal to change the amount of its deviation gradually in each scanning cycle.
However, in these prior art references, no consideration is made on the change of the angle .alpha. or the angle .beta. dependent on the kind of the tape or on the rotational speed of the rotating head.